Collins fragmentation function from gluon rescattering

Alessandro Bacchetta,Andreas Metz,Jian-Jun Yang

doi:10.1016/j.physletb.2003.09.005

Alessandro Bacchetta, Andreas Metz + Show 1 more

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https://doi.org/10.1016/j.physletb.2003.09.005

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Abstract

We estimate the Collins fragmentation function by introducing the effect of gluon rescattering in a model calculation of the fragmentation process. We include all necessary diagrams to the one-loop level and compute the nontrivial phases giving rise to the Collins function. We compare our results to the ones obtained from pion rescattering. We conclude that three out of four one-loop diagrams give sizeable contributions to the Collins function, and that the effect of gluon rescattering has a magnitude comparable to that of pion rescattering, but has opposite sign.

Highlights

The Collins fragmentation function [1] is an example of how the orientation of the quark spin can influence the direction of emission of hadrons in the fragmentation process
The Collins function is believed to be at the origin of single-spin asymmetries in hard hadronic reactions [2,3,4,5,6,7], which lead to attempts of estimating it from phenomenology [8,9,10,11,12]
We have computed all necessary diagrams contributing to the Collins function at the one-loop level, including the ones involved in the gauge link

Summary

Introduction

The Collins fragmentation function [1] is an example of how the orientation of the quark spin can influence the direction of emission of hadrons in the fragmentation process. Bacchetta et al / Physics Letters B 574 (2003) 225–231 the target spectators gives rise to T-odd distribution functions [15,16] This has been interpreted as the one-gluon approximation to the gauge link, which is included in the definition of parton distribution functions and insures their color gauge invariance [16,17,18,19]. It was soon realized that gauge link effects have different signs in semiinclusive DIS and Drell–Yan scattering [16,20], implying different signs for T-odd distribution functions in the two processes. As in the distribution functions, the gauge link can generate nontrivial phases and T-odd effects in the fragmentation functions as well. In that work only one of the four possible gluon rescattering contributions has been taken into account

Calculation of the Collins function

Numerical results

Conclusions